Spirophosphine-Catalyzed Enantioselective [3 + 2] Cycloaddition of Allenoates and Unsaturated α-Ketimine Esters

A novel chiral spiro-monophosphine, OUC-Phos, was synthesized and utilized for the first time in the asymmetric Lu's [3 + 2] cycloaddition reaction of β,γ-unsaturated α-ketimine ester with allenoate. OUC-Phos, featuring a 3,3'-diphenyl-modified spirobiindane skeleton, demonstrated exceptional catalytic efficiency in the [3 + 2] cycloaddition to achieve high yields, enantioselectivities, and diastereoselectivities for the targeted products. The broad substrate scope encompassing diverse functional groups demonstrated the versatility of this methodology. Furthermore, the reaction was successfully scaled up, and the products were easily converted into their corresponding functionalized derivatives.